1. Technical Field
The present invention relates to a technique of detecting the touch position of an object, such as a finger or a pen, on a screen.
2. Related Art
A liquid crystal display device that detects the coordinate position on a screen designated by a finger or a light pen is disclosed in JP-A-2004-318819. The liquid crystal display device includes an image reading sensor 33, which images incident light, for every pixel and detects the coordinate position from a change of imaging data when the finger or the light pen approaches or touches the screen. In addition, in the liquid crystal display device, the imaging data is not read from all image reading sensors 33 arrayed in a pixel array section 1, but is read for every four rows in the row direction and for every three columns in the column direction.
In the liquid crystal display device disclosed in JP-A-2004-318819, the coordinate position designated by the finger or the light pen is always detected at the same period. Accordingly, for example, when a detection period of the coordinate position is 60 Hz, it is not possible to trace the high-speed movement of a finger or light pen. This makes it difficult to smoothly input a handwritten image or the like by touch input. On the other hand, when the detection period of the coordinate position is about 120 Hz, it is possible to sufficiently trace the high-speed movement of the finger or light pen. In this case, however, the power consumption increases in proportion to the shortened detection period.